CPU Schedule – geeksforjobs


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  1. Arrival time : Process – >> Ready Queue
  2. completion time : Process completes its execution
  3. burst time: The time required by a process for CPU execution
  4. Turnaround time: Difference between completion time and arrival time (TAT = closing time – arrival time)
  5. Waiting time: Time difference between TAT and Burst Time (WT = TAT – BT)

Process determination objectives:

  1. Max CPU Utilization– Keep CPU as busy as possible
  2. Proper allocation of cpu
  3. Max turnaround time – Number of processes that complete their execution per unit time
  4. Min turnaround time – The time taken by a process to finish execution
  5. Min waiting time – Time waits in the ready queue =

Scheduling algorithm:

  1. FCFC
  2. STF – Shortest Burst Priority
  3. LTF – Longest Burst Priority
  4. SRTF – SJF’s earlier mode
  5. RTF – Preemptive Mode of LTF
  6. round robin – Each process is assigned a fixed time of Q quantum
  7. Priority assessment: Non-preventive (highest priority process is set first, starvation is possible)
  8. High response ratio next: Avoid starvation (response ratio = (wait time + burst time) / burst time)
  9. Multilevel queue: Processes are placed in separate queues according to priority. The high priority process is placed in the top-level queue. Only after the process is completed from the top-level queue, the low-level queuing processes are determined. It can suffer from starvation.
  10. Multilevel response queue: If a process uses too much CPU time, it is moved to a lower priority queue

Useful Facts:

  1. FCFS: Waiting for a long time
  2. SJF and SRTF: Causes Starvation
  3. SJF: optimal in terms of average waiting time

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